Semiconductor packages are used for protecting a semiconductor die in a package body, and providing connection points for connecting the packaged die to external devices. To cope with the high density and high pin-count of semiconductor chips, BGA and "flip chip" packages have been developed. In a typical BGA package, the semiconductor chip is mounted to the top surface of a printed circuit board type substrate. The chip is wire bonded to electrical traces in the substrate, then over-molded with an encapsulating material for protection. Solder balls are bonded to the electrical traces on the bottom surface of the substrate, serving as the external electrodes for surface mounting on a printed circuit board.
Flip chip packages are similar to BGA packages, except that the solder balls are attached directly to the bond pads or I/O pads formed on the surface of the chip. This results in a compact size of the flip chip packages. Because of the absence of an encapsulating material, flip chip packages are quite fragile and require careful assembly and handling techniques.
An example of a conventional flip chip BGA package that combines the durability of the BGA packages and the small size of the flip chip packages is shown in FIG. 1. In general, the conventional flip chip BGA package shown in FIG. 1 has some disadvantages. One is that chips are subject to damage because their top surfaces are exposed during testing or packaging steps. Another problem is that an external heat sink can not be easily and directly attached to the top surface of a chip. Furthermore, it is not easy to put an identification mark on the top surface of a chip.